The present invention relates to variable valve actuating system and method for an internal combustion engine equipped with variable valve timing control systems for intake and exhaust valves and an intake valve operation angle varying system, and more specifically to a fail-safe control technique at the time of malfunction in the exhaust variable valve timing control system.
For improvement in output and fuel consumption, and exhaust emission control of an internal combustion engine, a variable valve control mechanism is arranged to vary an intake or exhaust valve lift characteristic. A patent document 1 (Published Japanese Patent Application, Kokai No. H07(1995)-139378) discloses a valve actuation system arranged to decrease a valve overlap forcibly when a failure is detected in a control system for the variable valve timing mechanism, to maintain driving performance. A patent document 2 (Published Japanese Patent Application Kokai No. 2000-130196) discloses a system for decreasing or eliminating the valve overlap forcibly by controlling the operation of a valve operation angle varying mechanism for varying an intake/exhaust valve lift and operation angle when an abnormal condition is detected in an internal combustion engine. A patent document 3 (Published Japanese Patent Application Kokai No. 2003-49671) discloses a system which includes intake and exhaust variable valve timing control mechanisms. When an abnormal condition is detected in one of the variable valve timing mechanisms, this system controls the respective variable valve timing control mechanisms by using data for abnormal situation. For example, the system fixes the abnormal variable valve timing mechanism in the most retarded position and controls the other variable valve timing mechanism by using an operation map for the abnormal situation. Alternatively, both variable timing mechanisms are fixed at the most retarded positions.